Coextrusion has been widely described in the literature (including patents) as a technique for forming pressure sensitive adhesive laminates comprising one or more pressure sensitive adhesive layers and one or more backing layers. Again, reference is made to PCT publication WO 93/07228 in this regard although numerous other references could also be cited. According to FIG. 1B of WO 93/07228, a pressure sensitive adhesive tape comprising a backing or carrier layer; pressure sensitive adhesive layers on both sides thereof (illustrated in FIG. 1B) may be formed. FIG. 2 of this reference shows pressure sensitive hot melt adhesive streams (102 and 112) and a carrier stream (122) are supplied to a feed block (130) as a molten stream that combines into a single flow channel, which is then extruded through an extrusion die (140). The molten structure discharged from the extrusion die (140) can be cooled and laminated onto a release liner (150).
Foamed plastic, rubber and resin products are well known in the art. Such products encompass both a wide range of polymeric materials and a wide range of uses. Uses include, for example, structural materials, insulating materials (polystyrene foam cups, for example), just to name a few.
Foamed plastic materials are known as materials for both carriers (or substrates) and pressure sensitive adhesive layers in the pressure sensitive adhesive art, although the volume of prior art in this area is limited compared to the total volume of art on foamed plastics, rubber and resins generally.
U.S. Pat. No. 5,342,858 to Litchholt, et. al. describes elastomeric adhesive foams which are formed from an elastomeric, hot-melt adhesive material which is preferably pressure sensitive. Adhesive laminates are shown diagrammatically in Figure 1. Among these is an adhesive laminate in which an adhesive foam is formed on release paper (see especially Column 21, Line 51).
Adhesive laminates comprising pressure sensitive adhesive on a foamed thermoplastic backing layer are also known. See for example, published PCT International application WO 93/07228, published 15 Apr. 1993, especially Example 11 thereof. Pressure sensitive adhesive in this reference may be either foamed (see page 9, line 13 and 14) or non-foamed.
Foaming or blowing is invariably obtained by incorporation of a foaming or blowing agent into the polymer to be foamed prior to formation of any laminate. Foaming or blowing agents can be broadly classified as either chemical or physical. Chemical foaming or blowing agents form a foam or cell structure by decomposition of the foaming agent when decomposition temperature is reached. Physical foaming agents e.g., chlorinated hydrocarbons, ketones and alcohols, cause a cell structure to form by evaporation upon heating. Also known are gaseous foaming agents, which are incorporated into a thermoplastic mix at a higher pressure and foam formation results as the pressure is reduced. U.S. Pat. 5,342,858 cited supra (especially FIG. 2 and Column 11, lines 25 through 37, thereof) is illustrative of gaseous foaming agents.